The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A switched capacitor includes a network of a plurality of capacitors and switches, where the capacitors and the switches are connected in series, parallel, or a combination of both. The capacitors are charged and discharged by selectively opening and closing the switches. Switched capacitor circuits are used in many systems such as amplifiers, integrators, differentiators, adders, filters, comparators, data converters such as digital-to-analog converters (DACs) and analog-to-digital converters (ADCs), and so on. An example of a switched capacitor circuit is a switched capacitor DAC (capacitive DAC). Such a DAC may be stand-alone or embedded in a successive-approximation-register (SAR) ADC or a pipelined ADC. Switched capacitor based modulator circuits are also used in Sigma-Delta ADCs.
Cyclic or algorithmic analog-to-digital converters (ADCs) such as successive-approximation-register (SAR) ADCs, Sigma-Delta ADCs, and pipelined ADCs use a capacitive DAC as a core building block. For example, in a SAR ADC, during a conversion process, a capacitive DAC is periodically switched to generate analog voltage levels for comparison with a sampled input signal as part of a successive approximation algorithm. Specifically, inputs of the capacitive DAC are successively switched to either a reference voltage VREF or ground, thereby demanding charge from the reference voltage VREF. The amount of charge drawn by the capacitive DAC from the reference voltage depends on the input signal (i.e., input voltage) and is a function of a result or code generated by the conversion process. Accordingly, the capacitive DAC represents a code-dependent load that draws a code-dependent load current from the reference voltage.